EXPANSION TANK GUIDE
Within the system copper pipes are filled with heat transfer fluid (antifreeze). As the fluid is heated by the sun it expands, it is recommended to install an expansion tank in a closed loop system to allow the fluid to safely expand, otherwise it could damage the system.

An expansion tank allows the fluid in a closed-loop system to expand and contract depending on the temperature of the fluid. Without the expansion tank, the plumbing would easily burst when the fluid is heated. Diaphragm-type expansion tanks are constructed with an internal bladder and a pressurized air chamber. Heated fluid expands in the closed loop against the bladder and pressurized air chamber. As the fluid contracts while cooling, the air chamber maintains pressure in the closed loop. The size of the expansion tank must be able to handle the expansion based on the volume, coefficient of expansion, and range of temperature fluctuation. The size and number of collectors, and the size and length of piping and fittings determine fluid volume. Diaphragm-type expansion tanks are readily found in most plumbing supply businesses.